Hydraulic power circuit and control means



Feb. l8, 1941. E k E EK' 2,232,428

HYDRAULIC POWER CIRCUIT AND CCNTROL MEANS Filed March 3, 1957 Q ///lA A I Fig.1

[115K K BENEDEK .Patented Feb. 1941 UNITED STATES.

* PATENT OFFICE 2,232,421; maauuc rowaaciacm'rm comer.

- mum's a Elek K. Benedek, Bucyrus, Ohio Application March 3,1931, Serial No. 128,829 4 Claims. (01. 30-53) This invention relates to hydraulic pressure power circuits andrneans and methods for operating the same.,

One of. theprincipalobjects of the present invention is to provide a hydraulic circuit for operatively connecting a rotary, radial piston, variable delivery, reversible pump and a rotary, radial plunger, variable speed, reversible, hydraulic motor to provide a hydraulic transmission'mechanism.

Another object is'tc provide a hydraulic circuit in which novel cooperative relations between the pump and motor are provided and afford many advantages in the utilization of the transmission for locomotive vehicles and'the'like, and to enlarge the useful stroke of the motor.

For purposes of illustration, the circuit will be described in connection with a pump and motor operatively connected to provide a transmission mechanism for an automobile, the specific advan-" tag'es and operating characteristics of thecircuit I It is to be understood, however, that this embodibeing best illustrated by this concrete example.

ment is merely exemplary and the circuit is not to be limited to the particular use. illustratively described.

The present circult'is an entirely closed circuit as distinguishedfrom the customary by-pass circuits, and the advantages thereof will become more apparent from the following specification wherein reference is made to the accompanying drawing, in which: 1

Fig. 1 is a diagrammatic illustration ofthe cir-H cuit with the control valves therein; 4

Figs. 2 and 3 are diagrammatic sectional views. respectively, of a control valve suitable for use in the circuit and illustrating'certain operative settings thereof; p In order that the novelty and advantages of the present circuit may be understood more a brief description of-circuits of certain of my co- 1 pending applic tionsvwillbe given.

In my co-pe ding application Serial No. 5, 429

filed February 7, 1935, there is illustrated a closed hydraulic circuit connecting a variable delivery, one-way pump and a reversible variable speed motor. Such circuit includes a pressure line directly connecting the pump and motor and having a safety pressure relief valve leading to-a sump. and a low pressure or suction line directly connecting the pump and motor and having a branch leading from the sump and provided with an autoqmatic inlet check valve aflording only a one-way flow into the suction line from the sump. The flow.

through such 'a circuit isialways in thesame dipump at neutral.

, rection, and fluid is supplied from the sump only --to replace slip fluid or fluid discharged by the,

automatic relief valve. Reversal of operation of the resultant transmission is obtained. in thisv prior circuit by mechanically reversing the direc-K 5 'tion of rotation of the motor, the pump and motor being hydraulically lnterlockedat all times and the relief valve operating only duringlexcess pressure occasioned by shifting of the motor through its neutral stroke position. Such a cirr 10 cult, when used in a transmissionior a motor vehicle,-for example,- affords aipositive' but hy-- draulically elastic connection between the prime mover and the driven shaft, as a result of which the motor canbe used as a brake by setting the p In my co-pending application Serial N6; 85,550,

flied June 16, 1936, now Patent 2,098,214, issued November 9, 1937, there is illustrated a hydraulic motor designed primarily for rotary spindle ma go chines, comprising a multi-stage, reversible, variable speed motor and a reversible, variable deliv- In this circuit, the stages of the motor are con-. nected in parallel with each other and connected-25 to the pump. Leading from r each .of. the fluid 1 connections to the pump beyond the pump ports eflects cannot be obtained. This particular prior 46 circuit, using the multi-stage motor, isjprimarlly for over-speed and under-speed drive with a constant horse power cycle. The relief valves, being operative at predetermined pressures, make the structure ineifective for constant torque cycle. Thus, in this prior circuit, thehorse power're mains eonstant-during'any motor stroke and speed adjustment, whereas in the circuit in the present application, assuming constant power,

the minimum motor speed .is the same as "pump speed.

In my cc-pendingapplication Serial No. 92,259, filed May 18, 1935, nowPatent 2,163,079.- issued June 30, 1939, a reversibla variable, delivery pump to a reversible, variable multi- 1 stage motor in a non-reversible circuit, a set relief valve being provided in the pressure line of the circuit, and the suction line having no check valves or valves of any character, but being directly connected to the sump. also provides a constant horse power cycle as dis- .tinguished from a constant torque cycle such as by adjustment of the eccentricity of the reactance in the present application.

Referring next to thepresent circuit, the cit.-

cuit is shownin Fig. 1 in connection with a pump l which is of the rotary radial piston type and is reversible and variable in its delivery, both the reversal and variation in delivery being efl'ected member. The motor 2 ol! the resultant transmission is of the rotary radial piston type and is of variable speed and reversible, both the variation 7 in speed and reversal being effected by adjusting either as a motor.

the reactance member. The pump and motor are preferably identical in construction except perhaps that thejmotor is larger in size than the pump and either may be used as a pump and high to meet commercial requirements, and the weight, size and unit ratio of each is within or above commercially required limits. As exemplary oi the particular pump or motor, the same may-be such as disclosed in my copending application, Serial No. 27,558, filed June 20, 1935, now Patent 2,101,730, issued December 7, 1937, wherein the specific details of the same are disclosed and claimed. Such a reversible and e!- ficient motor is necessary-for rendering such a circuit operative and useful.

The pump discharges througha suitable conduit or pressure line 5 directly into the motor 2, the. operating fluid being discharged from the m described is preferably located entirely with-' motor through a return conduit'or line 6 which leads to the inlet side of the pump, thus providing a closed hydraulic circuit. As more fully described in my Patent 2,163,079, the circuit thus in a valve pi'ntle which is common-to both pump and motor. a conduit I which leads to a suitable sump I,

a cut-ofl valve 9 being provided in the conduit 1 between its connection with the return line 8 and thesump. To the pressure line 5 is connected a conduit Ill Jeading'to an automatic,

pressure relief valve Ii. The relief valve preferably comprises the usual bore in which operates a plug l2, the plug. being seated by a spring I: which is adjustable by a suitable screw ll. Connected to the valve II is a drain conduit 15 which returns the relief fluid to the sump 8.

A similar valve i8 is connected by'a'conduit I! to the return line G a drain conduit '20 leading the line 5 is the instantaneous pressure line and. the line I is the return line, the pressure fluid is delivered from the pump through the line 5 to the motor and operates the same and then returns to the pump through the line 6. Under such conditions the valve '9 is open and the valve 22 is closed so that, while the circuit is a closed circuit, fluid is admitted from the sump through theconduit I for replacement of slip andre- II to the sump. This structure The power. and torque ef- 'ficiencies or the pump and motor are sufdciently Connected to the return'line l .is'

\ arcane lie! fluid. It, for any reason, the pressure in the line I becomes excessive, it is relieved through the valve 1i and returns through the conduit 'l'hus, assuming the pump is driven in the direction indicated by the solid arrow 28 and the motor is driven in the direction indicated by the solid arrow 24, the circuit will operate as a safe and eiflcient closed circuit, the fiow. of fluid being indicated by the solid line arrows 28. With the same condition existing, the

motor can be mechanically reversed by reverseither direction for a given direction of operationby the pump.

0n the other hand, if the eccentricity of the pump is reversed so that its delivery is reversed, the line becomes the instantaneous pressure lineand the line 5 becomes the instantaneous return line. ,Concurrently with such reversal, however, the valve 9 should be closed and the valve 22 opened so that slip fluid can be supplied through the conduit 2i and excess pressurerelieved through the valve l8 and conduit 2!. This reversal of the delivery of the pump causes the flow through the circuit as indicated by the dotted arrows26- Under this reversed flow, the-direction of rotationof the motor can be reversed mechanically.

As more fully explained in my co-pending applicatiou Serial No. 716,451, filed March 20, 1934',

now Patent No. 2,166,717, issued July 18 1939, both the pump and the motor are provided with stroke adjusting means and two-directional adjustment; Each of the valves 9 and '22 is two-- Both the pump and the motor are reversible I hvdraulicallyas well as mechanically. In order to appreciate the advantages of the circuit, having in mind that'it is a closed circuit as distinguished from the less eiilcient by-pass circuit, the following operation should be noted.

a Ii both of the valves 9 and 22 are open at the same time, as illustrated in Fig. 1, it is apparent that there is no appreciable pressure in the circuit, but the circuit is at all times maintained filled with fluid by the pump. Accordingly, if

the motor is drivingly connected to the wheels of the vehicle, complete free-wheeling is obtained regardless of the operation of the pump. Assuming the vehicle is coasting, the motor temporarily becomes a pump. pumping into an open circuit regardless of its direction of operation. If, at the same time, the motor is concurrently set at zero stroke, even the slight resistance to flow occasioned by the open circuit is eliminated. During such operation, the pump of course will run idle with its prime mover and maintain the stantaneous pressure line, as during such opera-' t l, the has associated with'the open one 0! the valves becomes the return line through which 'the fluid is returned to the pump and slip is replaced.

If, during-such operation, the then open valve .is also closed without opening the already closed valve, both the pump and motor become inter-' locked hydraulically and a power braking efiect is obtained, limited only by the relief valves.

With the one of the valves 9 and 22 in the instantaneous return line open and the other closed, the operation may still be controlled by mentum of the motor and rearaxl'eof the car is subjected -to braking action. If the motor only isreversed, the engine which drives the pump is subjected to the braking force. Thus the pump can be made to brake the motor and the motor to brake the pump and connected engine. Assuming, for example, that the present inventionis utilized in an automotive vehicle. If the vehicle is operating down grade and the momentum of the car overtakes the driving eflect of the hydraulic motor M, the pressure in line I will gradually become zero, the motor speed eventually increasing beyond the driving speed of the prime mover and the operating speed of the pump. .This would result'in coasting .or freewheeling. with the motor running faster than the pump if the motor could-take in additional .fluid through the valve 22. But if the valve 22 is'closed, and also the valve 9;.the motor, having greater speed than the pump, will raise pres sure in line 6 against the moreslowly running pump. .The pressure raised in line 6 is proportional to the momentum of the car. Thus the,

motor is driven, not by the pressure power 'of the pump; but by the momentum of the'car. The.

resultant power developed .-by. the motor, which now acts as a pump, is "delivered to the pump,

causing the pump to act as a, motor against the prime mover and exert a braking'power against the forward drive rotation of the prime mover. In this way the excess power of momentum to the .car is transformed into dynamic. braking power. During this cycle, both the pump and the motor have reversed themselves automaticallyin operation, but not by stroke reversal.

Consequentlyynone of the relief valves, such as W H or ll, will discharge, but there will be arecircuit is closed entirely as long as the pressure versal of pressure from line 5 to line 6. Thus there is ajdiflerential pressure between lines 5 and 8 during this special cycle and it'is useful for braking the driving engine or prime mover. Thus, if both valves 9 and 22 are closed. the

remains below the working pressure of the relief valves. If, in this'condition of the circuit, the pump is set to zero stroke the motor becomes hydraulically locked. It might be mentioned that this .is'of greater importancein connection with a gun turret on battle ships than inconnection with automobiles, but it is important in either instance. v

If, in this condition of the circuit. reversal of the motor is required at full pressure it can be effected by shifting the motor reactance-memher, the respective pressure relief valves open- 3 ing in case oi temporary excessive pressure. This reversal of the motor can be accomplished-in a fraction of a second'because the pump is'continuously delivering fluid to the motor. If, on

the other hand, the reversal is to be effected by reversing the pump, the motor receives no pressure during the slip movement of the pump near pressure for operating the motor in one direc-;

tion until zero operation of the motor is established, and then the motor gradually builds up speed in the opposite direction. Thus, during pump reversal from one side of the rotative axis to the other, an idle pressureless period results, with the resultant loss of time and resultant back-lash in operating parts of themechanism and the apparatus driven thereby. S'uch backlash should be avoided in all. instances and in advantage. Of course there is a temporary pressure rise in the circuit when shifting the motor eccentricity, but this pressure is relieved through the valves, such as [I or it. In other words,

it is of greater advantage, in many instances, to have a temporary pressure rise rather than a temporary pressure drop. Consequently, the pump, as well as the motor, operates itself as a zero stroke and there is a gradual decrease of gun turrets it must be avoided. Consequently,

areversal of the motor directly is of extreme reversible valve in that reversal of the one of g the units which is then actingas a pump causes a reversal of flow in the circuit. The reversal of the motor, when his operating as a motor.

does not reverse the flow of the circuit but the effect of such reversal is the same as a reversing valve .which causes an instantaneous reversal of flow in the internal fluid circuit of the motor. fl

Thus, dynamic braking power is provided. Assuming, again, that a vehicle is operating down, grade, instead of closing both valves ,9

and 22, valve 22 may be open and valve lclosed,

thus reversing the circuit and developing pressure in line 6 by the motorwhile taking fluid into line 5 through the valve '22. Since the stroke of the pump is variable, it may be operated at just enough capacity so as not to brake the engine but only to brake the momentum-of the car. If under these circumstances, the pump and motor are working in opposition to each other, both draw fluid through the valve 22 and discharge it through the relief valve l8, and very effective braking is provided, dueto the restricted size of the relief valve passage of the relief valve. By adjusting the pump under these conditions, just the desired amount of braking power can be obtained. Y Next. if the valve I is open and the valve 22 is closed, with the pump delivering pressure" to' the motor through line 5, as soon as the momentum of thecar dominates thedriving'p wer and the motor thus reverses itself and acts as a pump,

the valve 9 may be closed and the valve 22 opened and the stroke of the pump reduced below the motor in such a manner that the motor willreceive part of the fluid from the pump and part through the valve 22, thus changing and controlling the dynamic braking power. With the valve 9 thus closed,'only the difference between thedischarge of the motor and the intake of the pump must be discharged through the relief valve it. Thus the relief valve does nothave to pass the differential between the capacity of the motor and the capacity of the pump. This amount.

is the same as the diflerential amount which is sucked through the open valve 22. Consequently,

70. all of the fluid pumped by the motor but only such,-for example, as automobiles and machine I tools.

-. Among the advantages obtained from the prescut circuit are the following: i a

1. The circuit may be used as. a positive power brake for decelerating or stopping the vehicle.

2. Free wheeling of the vehicle is possible. 3. The direction of rotation of the motor can be reversed intwo distinct ways: first, by shifting' the ,reactance member of the motor to the the direction of the motor without changing the direction of flow of liquid to it, and second,

by shifting the reactance member of the pump mg the engine itself. The braking of the engine is done so that the momentum of the car will be used topump enough fluid .to the pump to brake the pump and .engine or to make the engine slow down. Thus the stroke of the hydraulic motor will be established by adjustment to gradually slow down and brake the engine with its connected pump.

5. The cycle provided'when the motor becomes a pump due-to the forward movement of the ve- 40 hicle and pumps a ainst the force of the pump is one of the main advantages-of the double reversal. In such an instance, the motor will become a pump and the pump, under such circumstances, will be opposed by the fluid .pres- V sure developed by the motor sufficiently to slow or brake entirely the prime mover.

Further, it is apparent from the foregoing'description that the valves 8 and 22 may be mechanically connected to various operating levers m of the associated vehicle so as to be operated directly thereby, or may be operated by different control circuits related as desired to the operat-.

'ing characteristics of the particular vehicle.

When a pump and motor are included in a,

55 combination in a hydraulic circuit and both are of the same capacity, so long as the pump is kept at full stroke and full pressure, it will develop maximum horsepower and willoperate at a constant maximum. If the fluid thus delivered is so-passed to a motor of the same capacity, the motor will deliver a constant maximum horse power '|'0 ery decreases, but if the motor is kept at full stroke and the pressure is maintained constant for the given pump setting, the maximum power will be translated into maximum torque. There-. j

fore,- at-constant operating pressure, change of II pump stroke controls the power delivery while a If, however, the output volume of the I essence] I I I change of motor stroke controls the torque.

Attempts to control torque-by pump adjustment result in very ineflicient operation. 4 I

It is seen therefore that momentum of the car reverses both the pump and motor and if only one were reversible the transmission could not meet the conditions herein set forth. Under many conditions, it is only necessary that either the pump or the motor be reversed, but there are many conditions under which reversal of both simultaneously or independently is requiredand reversal of operation of the combination by reversing the pump is entirely'diiferent in the operating characteristics produced than is the.

reversal of operation effected by reversal of the motor. Pump reversal necessitates a dead period,

motor is likewise shown in connection with an. automotivevehicle. For instance, it makes posopposite side of dead center and thus reversing a ing and stopping, the pump can be set to zero.-

sible the elimination of a clutch because at start- If, for some reason, the car is stopped when the pump is at-zero and cannot be started, the car. I remains locked because any attempt to move it would cause the motor to operate as a pump and thus pump fluid in a blocked circuit. If, how-, ever, the motor can be set to zero, the car may be pushed or towed without subjecting any of the operating mechanism to any strain. It provides, in operating effect, the same results as are I provided by releasingthe clutch.

. In many instances, the motor is closer at hand for the operator than is the pump. Therefore.

the motor, which is more nearly within reach of the operator, is much easier toadjust. Here,

again, as in the case of a gun-turret, the pump accessible to the operator.- 'Again, since the pump replaces the clutch in a motor vehicle, it

must be capable of unloading. It is desirable for safety to reverse the motor while the pump is set to neutral so that during reversal of drive,

the engine is disconnected. If, as in conven-,

tional vehicles during the reversing shift, the engine is disconnected, there can be no mishap,-

even if the shift is wrong. until the engine is reclutched. But in a hydraulic circuit, shifting of the motor while the pump is set at neutral applied in the "on" direction in the same manner as engaging the conventional clutch, and a grad- ,conduits, a reversible variable displacement r'otary pump interconnecting said main conduits, a hydraulic motor connected between said main conduits, a sump, and manually operable means described my invention, what I for selectively connecting either or both of said main conduits to the lower part of said sump;

2. In a hydraulic transmission, a pair of main conduits, a reversible variable displacement rotary pump interconnecting said main conduits,

a hydraulic motor connected between said main conduits, a sump vented to the atmosphere, and

manually operable means for selectively ,con-

necting either or both of saidmain conduits to the lower part of said sump.

3. In a hydraulic transmission, a pair of main conduits, a reversible variable displacement rotary-pump interconnecting said main conduits, a reversible variable displacement hydraulic motor connected between said main conduits, a

sump vented to the atmosphere, and manually operable means for selectively connecting either or both of said main conduits to the lower part of said sump. a

4. In a hydraulic transmission, a pair of main conduits, a pump interconnecting said conduits, saidpump being capable of having the displacement thereof continuously varied from a maximum in one direction through zero to a maximum in the other direction while being continuously driven in one direction, a reversible variable displacement hydraulic motor connected between said main conduits, a sump vented to the atmosphere, manually operable means for selectively connecting either or both of said main conduits to the lower part of said sump, and pressure relief valves connecting said main conduits to said sump.

ELEK K. BENEDEK. 

